The invention relates to a centrifugal pump, in particular, a radial pump or a semi-axial pump including a housing with a pumping space and a dry space, a drive shaft rotatably supported in the housing and an impeller wheel firmly connected to the drive shaft for pumping a flow medium in the pumping space, and a shaft seal arranged in an inner radial area for sealing the dry space with respect to the flow medium wherein at least a part of the shaft seal is held in position by a seal cover connected to the housing.
A centrifugal pump of this type for pumping a liquid flow medium is used in particular for pumping sea water in ships. In such an application, a centrifugal pump of the type referred to above is exposed to comparably high stresses. Still a reliable operation is necessary even after an extended shutdown.
It is a problem with centrifugal pumps for pumping a liquid flow medium that a shaft seal during initial operation of the pump is not contacted by the flow medium, that is, it is in a comparably dry state. This affects the shaft seal in a disadvantageous way. The dry state during operation of the centrifugal pump for pumping the liquid flow medium may result from a condition whereby the shaft seal is not in contact with the flow medium because of air in the flow medium. It has been found that during starting operation particularly of radial pumps or semi-axial pumps the liquid flow medium moves along the radially outer areas because of the centrifugal forces whereas the air content collects in the radially inner area that is around the shaft seal. Such dry run operating states of a centrifugal pump can have substantial disadvantages for the shaft seal such as insufficient lubrication and/or cooling of the shaft seal by the flow medium. As a result, there may be increased wear of the shaft seal which reduces the life of the shaft seal. In a worst case, with an insufficient lubrication and/or cooling, tensions in the material of the shaft seal can detrimentally affect other parts of the centrifugal pump and may result in irreparable damages.
It would be desirable to avoid the detrimental effects of dry running states experienced by centrifugal pumps.
It is therefore the object of the present invention to provide means by which the durability of centrifugal pumps is increased and, specifically, dry running conditions of a shaft seal are largely avoided even during startup operation of the pump.